This invention relates to a process of producing fine-grained coke by degasification of fine-grained coal. The coal to be degasified is mixed with recirculated, heated, fine-grained coke in a mixer, particularly a double-blade mixer having two shafts rotating in the same direction, the gases and vapors which are produced are withdrawn from the top portion of an intermediate bin, which is disposed below the mixer, and are subjected to a mechanical dust collection and then to fractional condensation.
When fine-grained coke is produced by a degasification of coal at elevated temperatures, recirculated fine-grained coke or hot gas is used as a heat carrier. In the latter case, the process may be carried out in an entraining gas stream or in a fluidized bed. Here, the hot gases are produced by the combustion of gas or coke and the combustion gases dilute the gases and vapors which are evolved from the coal and render the cooling of the gases and the condensation of the tars more difficult.
If fine-grained coke is used as a recirculated heat carrier, the coal gases will remain undiluted, the high calorific value of the gases will be preserved and smaller condensing means may be used.
The process of degasifying coal with the aid of coke as a recirculated heat carrier has proved highly desirable in plants which have a high production rate and serve to produce coke for sintering purposes, or as a leaning coke for coking plants, or particularly for making shaped coke bodies. The coke which is produced in the process itself is preferably used as recirculated coke. Such a process is described, for example, in DOS 1,809,874.
A problem involved in the previously described process resides in the fact that high-boiling tars produced by the condensation of the coal gases have now a low market value because they contain residual dust and differ from the tar which is produced in the conventional by-product coke-oven. They are more aliphatic and naphthenic and less aromatic. For this reason, it might be desirable to utilize the high-boiling tars in the process itself as far as possible.
In the process disclosed in DOS 1,809,874, a dry distillation of bituminous or oil-containing materials is effected by recycling a high-dust fraction of the condensed heavy oil to the dry distillation reactor and redistilling at medium temperatures. This distillation serves to remove the dust which is contained in the heavy oil produced in the first condensing stage.
DOS 1,909,263 also describes a process in which heavy oil from the first condensing stage is recycled to the dry distillation reactor. In that case, too, the heavy oil is recycled so that the dust is removed by distillation. In both of these processes, the redistillation is in most cases accompanied by an undesired secondary effect which is a slight cracking of the heavy oil.